1. Field of the Invention
The present invention relates to a method for forming a pattern, and more particularly, to a method for forming a pattern of a liquid crystal display device.
2. Description of the Related Art
Cathode ray tube (CRT) monitors have been commonly used for displaying information on television and computer displays. Although the CRT monitors have high image quality and brightness, as sizes of image screens increase, a depth of the CRT monitor increases to occupy very large volumes. In addition, the weight of the CRT monitors has always been problematic in portable devices.
Flat panel display devices, such as liquid crystal displays, plasma display panels, organic electro luminescence displays, light emitting diodes, and field emission displays, have been used to replace the CRT monitors. Among these different flat panel display devices, the liquid crystal display (LCD) devices are commonly used as monitors of notebook and desktop personal computers because of their low power consumption.
FIG. 1 is a cross sectional view of an LCD device according to the related art. In FIG. 1, the LCD device includes a lower substrate 10, an upper substrate 20, and a liquid crystal layer 15 formed in between the upper and lower substrates 10 and 20. A thin film transistor T and a pixel electrode 7 are formed on the lower substrate 10, wherein the thin film transistor T include: a gate electrode 1 to which scan signals are supplied, a semiconductor layer 3 for transmitting data signals corresponding to the scan signals, a gate insulating layer 2 for electrically isolating the semiconductor layer 3 and the gate electrode 1, a source electrode 4 formed on an upper part of the semiconductor layer 3 for supplying the data signals, and a drain electrode 5 for supplying the data signals to the pixel electrode 7. The semiconductor layer 3 comprises an active layer 3a formed of amorphous silicon (a-Si), and an n+ doped ohmic contact layer 3b formed on both upper sides of the active layer 3a. A passivation layer 6 and the pixel electrode 7 are formed on the thin film transistor T, and a first alignment layer 4a formed for aligning liquid crystal molecules is formed on an upper part of the pixel electrode 7. The pixel electrode 7 is formed of a transparent conductor, such as indium tin oxide (ITO) or indium zinc oxide (IZO), so that the light can be transmitted through the pixel electrode 7.
A black matrix 12 is formed on the upper substrate 20 for preventing the light from leaking between adjacent pixels, and color filters 11 of red (R), green (G), and blue (B), for producing colored light, are formed on the black matrix 12. A flattening layer (not shown) can be additionally formed on the color filter 11 for flattening the color filter and for improving an adhesive bond to a common electrode 13 subsequently formed on the color filters 11, wherein the common electrode 13 applies a voltage to the liquid crystal layer 15 and is formed of a transparent conductor, such as ITO or IZO. In addition, a second alignment layer 4b, for aligning the liquid crystal molecules, is formed on the common electrode 13.
During fabrication of the LCD device, several steps of thin film deposition and photolithographic processes should be performed. For example, in order to fabricate the thin film transistor T, the color filters 11, and the black matrix 12, photoresist patterns are formed by application of a photoresist material, exposure and strip processes using a mask from the photoresist patterns, and an etching process using the photoresist patterns as a mask. However, the photoresist forming process involves complex fabrication processes and is not suitable for a large area display device. Thus, a printing method by which patterned photoresist can be formed simply without the exposure process has been developed.
FIGS. 2A to 2C are schematic cross sectional views of a fabrication process according to the related art. In FIG. 2A, a cliché 24 with a concave groove 23 formed at a position corresponding to a pattern desired to be formed on a substrate is prepared. Then, a resist 31 is deposited on a surface of the cliché 24. Next, a doctor blade 32 is placed in contact with the surface of the cliché 24 and flattens the resist 31 across the surface of the cliché 24. Accordingly, the resist 31 fills the groove 23 while the resist remaining on the surface of the cliché 24 is removed.
In FIG. 2B, the resist 31 filled in the groove 23 of the cliché 24 is transferred onto a surface of the printing roll 33 as the print roll 33 rotates across the surface of the cliché 24. The printing roll 33 is formed having the same width as a width of a panel of a display device desired to be fabricated, and has a circumference equal to a length of the panel. Accordingly, the resist 31 filled in the groove 23 of the cliché 24 is transferred onto the printing roll 33.
In FIG. 2C, the resist 31 previously transferred onto the printing roll 33 contacts a surface of the substrate 30 as the printing roll 33 is rotated. Then, the resist 31 is transferred from the printing roll 33 onto the surface of the substrate 30. Next, the applied resist 31 is UV-irradiated or heated to be dried to form a resist pattern.
However, in the LCD devices, pattern sizes differ according to different layers that are to be formed, and differ for the same layers. In addition, although the pattern sizes determine a viscosity of the resist to be used, resists of different viscosities cannot be printed at one time. Thus, a resist having viscosity suitable for a pattern of a corresponding size has to be selected. When using a resist suitable for a relatively small pattern, when the resist is filled into the grooves of the cliche and flattened by the doctor blade, the resist is removed more easily at a center portion of the cliché than at edge portions of the cliché. Accordingly, the thickness of a pattern is not uniform.
FIGS. 3A and 3B are schematic cross sectional views comparing resist patterns according to the related art. In FIG. 3A, a normally printed resist pattern 35a is formed on the substrate 30. In FIG. 3B, an inferior resist pattern 35b is formed on the substrate 30. As shown, the normally printed resist pattern 35a has a uniform thickness, wherein thicknesses of the inferior pattern 35b varies at the ends and middle portions. As a result, the inferior resist pattern 35b causes fabrication of a defected LCD device.